-0.92
Values in a normal table are usually given for z = 0 to 3 or 4.
Negative values are calculated by symmetry.
Between z = -0.28 and z = 0.64 it is the sum of the values for z = 0.28 and z = 0.64 (using tables to 4 dp):
z = -0.28 → 0.1103
z = 0.64 → 0.2389
→ probability of a value of z between -0.28 and 0.64 is 0.1103 + 0.2389 = 0.3492
The probability is 0.34915, approx.